This invention relates to microprocessor systems, and more specifically, to a clocking control circuit for controlling the operation of a microprocessor used in a power-limited environment, such as in a medical implanted device.
Among many uses of miniature electronic data processors, more commonly known as microprocessors, is to control monitoring and diagnosing circuits in implanted medical devices. They are particularly desirable because of their relatively small weight and size. In each application, however, the microprocessor requires a certain amount of power and the power demand varies according to the amount of "processing" activity performed by the microprocessor. By "processing" activity, it is meant data transfers into and out of various registers in the microprocessor and computations or logic operations performed by the processor. For use in medically implanted devices, a storage battery usually provides the source of power for the microprocessor operation, but if the battery becomes exhausted, then it becomes necessary to surgically replace the battery to maintain the electrical functions performed by the microprocessor.
One obvious approach for minimizing the foregoing difficulties is to employ microprocessor logic requiring a minimum amount of power and/or to employ extended-life, durable batteries. The advantage gained by these techniques are limited by the state-of-the-art in solid state logic and battery design. Another rather obvious approach for extending the useful life of the microprocessor power source is to turn-off power to non-essential circuits at certain time periods that do not require the affected electronic circuit, but in the case of a microprocessor controlled device, such as a data acquisition device, this may not always be possible since internal housekeeping functions require continuous operation for timekeeping, data logging, and other monitoring and control operations. Also, some types of logic circuits essential to the operation of the processor unit, such as an active memory, require repetitive refreshing cycles in order to retain the validity of their data content. Refreshing cycles requires continuous power which cannot be temporarily suspended. A significant amount of power, however, could be conserved by deactivating the processor during idle periods, such as between transfers of memory data or executions of instructions. But since the microprocessor itself is usually the sole unit within a data processing system that controls all other devices (such as peripherals and memories), it is not ordinarily powered down as synchronism in operation with the other devices could be lost.
In view of the foregoing, an objective of the present invention is to provide a clocking control circuit for reducing power requirement of a microprocessor operated in a power-limited environment.
A more specific objective of the present invention is to provide a clocking control circuit for starting and stopping a microprocessor clock at an optimum phase during its instruction cycle, thereby to reduce power drain during idle periods and to preserve its synchronism with other devices when restarted.
A further objective of the present invention is to provide a clocking control circuit for use in a microprocessor system that includes a random access memory which circuit enables the use of the memory by other peripheral devices in the system when the microprocessor is idle.
Other objects of this invention will become apparent upon review of the succeeding description of an illustrative embodiment.